Is it OK ... to have an open fire?

The Buncefield fuel depot explosion was a poignant visual reminder of just how great an effect the burning of fossil fuels has on our skies: to put the emissions into perspective, the amount of fuel that ignited is roughly one-eleventh by volume of what the US consumes in just one day.

The effects of air pollution will be familiar to a generation of London residents who suffered the city's debilitating smogs, particularly the Great Smog of early December 1952, which claimed at least 4,000 lives. Over the following decades, regulations such as the various Clean Air Acts greatly reduced the burning of coal in homes and coincided with the mass installation of central heating systems. As if to highlight the shift in pollutants in the air over this period, the last significant London smog, that of December 1991, was caused by traffic fumes, not domestic fires.

Many homes, particularly older housing stock, still have fireplaces and the aesthetic, comforting allure of an open fire remains a strong one. Some homes, though, especially those in urban areas, are now located in smoke control areas (check your area at www.uksmokecontrolareas.co.uk). This means that the burning of regular house coal and logs, with some exceptions, is outlawed. "Smokeless" coal is allowed, but, like the gas or oil used to run most central heating systems, it is still a fossil fuel, with similar consequences for climate change. So, if you do live in an area where logs can be burnt, are they a better option?

The truth is that whatever fuel you burn in a hearth, it is an extremely inefficient way to heat a room. As much as 90% of the heat will go straight up the chimney. Open fires also increase draughts: an open fire can draw up to 17 cubic metres of air a minute and will get it from wherever it can.

But at least logs are from a renewable source in the sense that you are only releasing the carbon dioxide that was "captured" as the tree grew. In contrast, the CO2 in coal has been safely locked underground for millennia and is therefore not part of the planet's current natural carbon cycle. Also, logs are typically sourced locally (if possible, best sourced from a local tree surgeon, or from dead trees that have fallen), whereas, following the mass closure of collieries in this country, more and more house coal is being imported from countries such as Colombia and Indonesia. Even smokeless coals such as anthracite, although still being mined in Wales and Scotland, are increasingly being imported from China, Vietnam and South Africa.

While logs should always be preferred to coal, it is true that coal gives off much more heat by weight: coal has a calorific value of about 27 gigajoules (GJ) a tonne compared to 7-11GJ a tonne for logs. But there are ways to get the most from your logs. Seasoning them is crucial. When a tree is first felled its timber can contain as much as 60% water, especially if it's a conifer (broadleaf trees makes much better logs). But if they've been air-dried for a year then brought indoors a few weeks before being used, their calorific value can increase by up to 50%. Seasoning also greatly reduces the amount of smoke logs emit when lit. (Household pollution is a key drawback of open fires, and has been linked to increased occurrences of respiratory illnesses, especially in children and the elderly.)

Increasing surface area by chopping logs to a diameter of about 10-15cm can increase efficiency too. So can burning smaller, hotter fires by allowing each log to burn right down before placing on another. To increase efficiency further, coal grates should be replaced by solid metal base plates and chimneys should also be swept twice a year.

But if you are using an open fire as your main source of heat and not just, say, to heat a living room on the coldest of days, the best option by far is to consider installing a wood stove. The latest generation of stoves can even heat radiators by using back boilers. Contact the National Energy Foundation (www.nef.org.uk/logpile, tel: 01908 665555) for more details

You say ...

Certainly not. Open fires are appalling inefficient; whether coal, gas or wood is being burnt, very little of the calorific value of the fuel reaches the room and they draw vast quantities of air up the chimney, even when they are not in use. Even if a carbon-neutral fuel like wood is being burnt they waste fuel and add to CO2 emissions. Closed stoves are much better, but still not as efficient as a condensing boiler.Alan Kennedy, by email